As pack 'H' is working from left to right on the passed string, you can simply say pack 'H2' (two hex characters make up one byte):

sub get_bytes {
    return join '', map {
        pack('H2', $_)
    } split /-/, $_[0];
}

print get_bytes('66-6f-6f00-62ff-61-72');
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This would print "foobar", because the lower bytes 00 and ff are being ignored.